The invention relates to a method for adjusting a radar sensor mounted on a motor vehicle having three radar beams emitted in a fan-shaped manner, one of which extends centrally and the other two extend laterally at the same angle.
The use of this type of radar sensor is expanding. The sensors are implemented in the field of ACC (Automatic Cruise Control) devices for ascertaining the distance of the vehicle from the respective preceding vehicle, and maintaining a constant distance by controlling the drive units appropriately. A presupposition for proper function is an exact adjustment of the radar sensor relative to the longitudinal axis of the vehicle. This adjustment must be made prior to the initial system startup, that is, during the manufacture of the vehicle or in the assembly phase. The problem associated with this condition is that a possible misalignment by a few degrees is not externally perceptible, but can have a considerable impact on the functioning capability of the overall system. If a misalignment has occurred, the system perceives vehicles traveling offset ahead as being located immediately in front of the vehicle, while interpreting vehicles located immediately in front of the vehicle as traveling offset ahead.
The prior art is affected by the following problems:
(1) The reflector plate must be oriented perpendicular to the vehicle axis, both in the vertical and horizontal directions. The use of a common reference plane for the vehicle and reflector can assure the vertical orientation.
(2) If the reflector is oriented perpendicular to the vehicle axis, the signals received in all of the radar channels (e.g., the left, center and right lobes) are compared to one another. If the reception amplitude of the right lobe is stronger than that of the left lobe, for example, it can be safely assumed that the sensor has become misaligned to the left; the extent of the misalignment angle cannot be determined, however. The prior art is therefore a process of xe2x80x9ctrial and error.xe2x80x9d After the direction of the misalignment has been determined, the mounted position of the sensor can be corrected by an arbitrary angular distance, and the measurement is repeated, until the operational sign of the misalignment angle changes. This iterative process is extremely time-consuming, and is hardly suited for mass production.
It is the object of the invention to provide a method of the above-mentioned type, which permits a simple, exact adjustment of the radar sensor.
The invention accomplishes this object by providing a method for adjusting a radar sensor mounted on a motor vehicle comprising three radar beams emitted in a fan-shaped manner, one of which extends centrally and the other two extend laterally at the same angle. A reflector plate mounted at a distance from the motor vehicle and vertically in relation to the longitudinal axis of the vehicle is rotated around a vertical axis. The deviation of the angular position of the reflector plate from an ideal position is determined, in which position both lateral radar beams supply an at least approximately equal reflection signal. The radar sensor is then rotated at a correcting angle that is inversely equal to the angular position deviation of the reflector plate.
The invention is based on the following concepts:
(1) The horizontal orientation of the reflector through the measurement of the distances between the rear wheels and the reflector, and the use of this information to calculate the vehicle""s skew angle relative to the reflector.
(2) The use of a reflector that can pivot by arbitrary angular distances about a horizontal and a vertical axis. The mounted position of the sensor must be corrected after the final vertical and horizontal misalignment angles have been determined. Additionally, the evaluation unit for the radar signals and the adjusting mechanism of the reflector plate are coupled to one another, which allows for a fully-automated procedure that requires no manual intervention.